SNAKES, LIZARDS, TURTLES, AND CROCODILES 263 



terrestrial. The term turtle is usually applied to the aquatic 

 forms, while the land forms are commonly known as tortoises. 

 The name terrapin is applied to some of the kinds that are used 

 for food. They all lay eggs, which may be deposited in the 

 banks of the ponds, rivers or streams, or in the sand, where 

 they are incubated by the sun's rays. 



Turtles, tortoises and terrapins are of considerable economic 

 importance as some of them are highly valued for food. Also 

 the horny carapace of many species is very valuable, being 



FIG. 119. -The giant land-tortoise of the Galapagos Islands, Testudo sp. 

 (These tortoises reach a length of four feet; after Coleman.) 



used extensively in the manufacture of combs and various 

 ornaments. Among the common aquatic species found in 

 the United States are the soft-shelled turtles, genus Trionyx. 

 The flat leathery shell as well as the enclosed body are used for 

 food. The animal defends itself viciously when attacked. 

 The large snapping-turtle, Chelydra serpentina, that is found in 

 so many of the streams and ponds east of the Rocky Mountains, 

 defends itself principally by its powerful beak as its shell is too 

 small to protect it completely. The southern alligator snap- 

 ping-turtle, Macrochelys lacerlina, often attains a weight of 



